Analysis of immunoreactivity to a Streptococcus equi subsp zooepidemicus M-like protein to confirm an outbreak of poststreptococcal glomerulonephritis, and sequences of M-like proteins from isolates obtained from different host species

The etiologic agent of a large 1998 outbreak of poststreptococcal acute glo merulonephritis (PSGN) in Nova Serrana, Brazil, was found likely to be a sp ecific strain of Streptococcus equi subsp, zooepidemicus from contaminated cheese (S. Balter et al., Lancet 355:1776-1780, 2000). In the present study , we used a serologic screen for a known surface-exposed virulence factor t o confirm the epidemiologic findings. Using primers Banking a previously ch aracterized M-like protein gene (J. F. Timoney et al., Infect. Immun. 63:14 40-1445, 1995), we amplified and sequenced the M-like protein (designated S zp5058) gene and found it to be identical among four independent acute-phas e PSGN patient isolates. Convalescent-phase sera from 33 of 44 patients in the PSGN outbreak were found to contain antibodies highly reactive to a pur ified Szp5058 fusion protein, compared with 1 of 17 control sera (P < 0.000 1), suggesting that Szp5058 was expressed during infection and further impl icating this strain as the cause of the PSGN outbreak The predicted signal sequence and cell wall association motif of Szp5058 were highly conserved w ith the corresponding sequence from S. equi subsp. zooepidemicus SzpW60, wh ile the predicted surface-exposed portions differed markedly between these two proteins. The 5' end of the szp5058 gene, including its variable region , was identical to the szp gene from another strain associated with a previ ous PSGN outbreak in England (M. Barham et al., Lancet i:945-948, 1983), an d the corresponding szp sequence found from the Lancefield group C type str ain isolated from a guinea pig. In addition, the hypervariable (HV) portion of szp5058 was identical to a previously published HV sequence from a hors e isolate (J. A. Walker and J. F. Timoney, Am. J. Vet. Res. 59:1129-1133, 1 998). Three other strains of S. equi subsp. zooepidemicus, including anothe r strain previously associated with a PSGN outbreak, were each found to con tain a distinct szp gene. Two of these szp genes had HV regions identical t o szp regions from isolates recovered from different host species.